Radio paging systems and mobile radio telephone systems are well known and widely used. Upon receipt of a page, radio paging systems provide a user with audio and/or visual information from the paging party, but cannot transmit information back to the paging party. Recently, national and international paging services have been implemented so that individuals may receive a page throughout the United States or throughout Europe. Despite the advances in paging technology, a significant disadvantage of radio paging is that after an individual carrying a pager has learned that a paging party wishes to communicate, that individual must locate a telephone communication system to contact the paging party.
Radio paging systems typically include a radio transmitter for transmitting a coded, radio frequency signal associated with a party to be paged and a portable paging receiver. To contact a party carrying a pager, a person dials a telephone number. The number is transferred by the Public Switching Telephone Network (PSTN) to the radio transmitter. The transmitter transmits a page signal coded to all pagers in the range of the transmitter. Because each mobile pager responds to a different paging signal, only the pager having a code corresponding to that transmitted is activated. The activated pager generates an audible tone or some other signal to notify the designated party that he or she has been paged. That party typically responds by calling a specific telephone number to receive further instructions.
One advantage of paging systems is that they can serve relatively large geographic areas. Another advantage is that a paging subscriber may be reached anywhere in the transmitter coverage area without knowing the location of that subscriber. As described above, the major disadvantage of paging systems is that a subscriber cannot immediately communicate with the persons who initiated the call. In fact, the subscriber cannot even acknowledge that he has received the page.
In contrast, mobile radio telephone systems allow flexible, two-way radio communications with a plurality of mobile subscribers. Cellular telephones allow subscribers to be paged immediately over cellular paging frequencies (as long as the phone unit is "on") via the wired telephone network. The mobile telephone responds immediately to a page in order to capture a voice channel for the communication. In addition, subscribers may initiate calls themselves. Unfortunately, mobile telephones cannot be paged while the mobile telephone is "off" or deactivated. To keep the mobile telephone activated continuously in order to monitor a cellular paging channel imposes a significant drain on the mobile telephone battery. As a result, large, bulky batteries are required.
Although mobile telephones have a greater number and variety of functions as compared to pagers, with respect to the paging function, pagers require less battery power. Attempts have been made to reduce the size and the weight of mobile telephone batteries, in particular, the batteries of hand held mobile telephones. Specialized techniques have been developed in conjunction with these reduced batteries. One method is discontinuous transmission (DTX) where the sender draws current only when speech is actually transmitted. Another method is discontinuous reception (DTR) where paging occurs at predetermined intervals known to the mobile and the land system with the mobile receiver being turned off during inactive periods. Nonetheless, battery size and weight in hand held mobile telephones are still a considerable problem.
In the near future, dual mode mobile telephones will be introduced into the U.S.A. according to the EIA/TIA Standard IS-54 which are capable of communicating over both analog and digital voice channels but use analog control channels. While the next generation of mobile telephones will include purely digital mobiles communicating over digital voice channels only and using only digital control channels, most of these digital mobiles will be hand held telephones and will be used in the cities. It is likely that the mobile telephone base stations in rural areas will remain analog for quite some time. In that situation, the radio coverage for digital mobile stations will be less than it is for pagers. Thus, it is desirable to take advantage of both cellular and traditional paging services.
One disadvantage with cellular telephony is that a subscriber's location must be known to the cellular system. Subscriber location is achieved by registering each mobile periodically. In contrast, paging systems do not require individual pagers to register. Thus, paging services are advantageous in situations where a subscriber desires to keep his exact location secret but still wants to have the option of being contacted.
Recently, it has become possible to subscribe to a cellular service and to an independent paging system. Telephone calls from the land-based telephone network are attempted initially with the mobile station over the cellular network. If the subscriber does not answer, the call is diverted to a FM radio paging system.
A cellular pager is disclosed in U.S. Statutory Invention Registration H610 to Focarile et al. In this system, a separate paging system is used in conjunction with the cellular telephone system. The paging system provides a backup for cellular telephone calls intended for an associated cellular telephone which has been deactivated because the subscriber is, for example, temporarily away from his automobile. Assigned the same number as the associated cellular telephone, the pager provides an alert signal to the subscriber of the cellular telephone indicating that a caller is trying to reach the telephone's assigned number. Later, the subscriber may call an appropriate service number for the information when the subscriber returns to the automobile and activates the cellular telephone.
Another system combining paging capabilities with a cellular system is disclosed in U.S. Pat. No. 4,748,655 to Thrower et al. In addition to conventional cellular components, the Thrower patent incorporates a pocket-sized, radio telephone for short range, low-powered communication with the cellular system over various "gateway" devices, e.g., a mobile radio telephone set. These pocket-sized phones are similar to cordless telephones which communicate with the gateway devices using low-power transmitter/receiver units. The portable telephone transmits its identification number to the gateway device which transmits the portable telephone's identification number and location via the base station to the mobile switching center of the cellular network. When the subscriber is out of range of a gateway device or does not have a gateway device, his portable telephone can operate as a paging device from a separate paging station. However, because of the portable telephone's low power, the subscriber is unable to communicate back with the paging station.
The prior art attempts to integrate paging and cellular communications systems are not always convenient to the subscriber and efficient in terms of battery consumption. Focarile's system requires a subscriber to carry an activated paging device around as well as an activated mobile telephone. This situation is burdensome and wastes considerable battery power. Moreover, if only the paging device is activated, the subscriber can only be reached by dialing his page number. Once paged, the subscriber must activate his mobile telephone, dial a message center, retrieve the message/number, and call back the paging party. Similarly, a major drawback of the Thrower system is that it requires, in addition to standard cellular components, cumbersome, portable phone and gateway circuitry which are energy inefficient and relatively expensive.